Patent GB-581165-A (GB)
Title: Method of and apparatus for the detection by electro-magnetic radiation of the presence and location of objects in space
IPC: G01S1/02
Filed: 1941-04-01
Abstract: 581,165. Radiolocation ; Wireless systems ; receivers. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., FURNIVAL, J. M., RUST, N. M., and PARTINGTON, G. E. April 1, 1941, Nos. 4375 and 11151. [Class 40 (v)] A radio reflection detector comprises a superregenerative trans-receiver having means for generating and transmitting ultra-high-frequency oscillations, means for periodically quenching at a variable frequency the oscillations generated, means for receiving oscillatory energy reflected by an objective body and for controlling in accordance with received energy the amplitude of the oscillations generated, and a device for detecting relative movement between the radio reflection detector and the objective body. The reflection detector may also include means calibrated in units of distance for varying the frequency of the periodic quenching. The amplitude of the generated oscillations indicates distance, while periodic change in the relations between the transmitted and received waves indicates relative velocity. The trans-receiver consists of an ultra-highfrequency oscillation generator, a quenchfrequency generator, and an audio-frequency detector. The ultra-high-frequency oscillation generator includes a valve V1, Fig. 1, having a quarter-wave hairpin line B between one leg of the filament and the positive terminal 6v of a source of filament heating current. A quarterwave aerial A is connected to the bend of the line B. Between the other leg of the filament and the earthed negative terminal of the source of heating current is a short-circuited coaxial line CL1, to the inner conductor of which the cathode is also connected. Between the control grid and earth is an open-circuited coaxial line CL2 and resistances r, Rg constituting the grid leak. The anode is connected through a small condenser C1 to the earthed outer conductor of the coaxial line CL2 and is also connected to the positive supply source +300V through an ultra-high-frequency choke F. The quenchfrequency oscillation generator includes a condenser C2, the primary winding La of a reaction transformer, the choke F, the valve V1 and the coaxial line CL 1. The secondary winding Lg of the reaction transformer is tuned by a variable condenser Cg, this tuned circuit being connected by means of a blocking condenser C4 between the junction of the resistance r, Rg and the earthed end of the line CL1. A radiofrequency choke RFC is connected between the choke F and the positive terminal +300V. For the detection of signals picked up by the trans-receiver an audio-frequency choke LFC is provided. Audio-frequency voltages produced across this produce currents in the primary winding of a transformer T, the secondary voltage of which is amplified in a valve V2 and applied to a loud-speaker LS. In order to ensure a constant phase-time position of the ultra-high-frequency oscillations generated by the trans-receiver a locking circuit is provided. This comprises an ultra-high-frequency oscillation generator operating at substantially the same frequency as the trans-receiver, and may include an audio-frequency modulator so as to produce a musical tone. The oscillator of the locking circuit includes an acorn valve V3 having ultra-high-frequency chokes Uhf in the filament leads and short wires forming a transmission line TL between the grid and anode. This is terminated by a variable condenser Ct for controlling the frequency of the oscillations produced. Anode modulation of the oscillations is provided by means of a tone frequency generator including a valve V4. A variable series anode resistance Rt varies the high tension and therefore the strength of the oscillations. The locking circuit is mutually coupled to the trans-receiver. The strength of the locally injected signal is controlled by varying the coupling or the resistance Rt. The second harmonic of the locking circuit provides the de-sensitizing signal. The quench-frequency gives a rough indication of the distance if varied to maintain a constant amplitude of the generated energy. The pitch of the note produced by auto modulation indicates the instantaneous speed of relative movement. Increase of range may be obtained by increasing the amplitude of every nth pulse of transmitted energy. A number of ranges of quenchfrequencies may be obtained by substituting different values of the primary and secondary windings La. Lg and the condenser C4 by means of a multiple-arm switch. Two projectors P1, P2, Fig. 7, may be provided for projecting two overlapping beams which may be characterised by the morse code letters E and T. Comparison of received energy from the two beams may be effected by means of a mechanical or electronic switch S automatically or manually controlled. The output of the trans-receiver A is integrated and applied to a central-zero visual indicator V1, which may be interconnected with the switch S to give a sense of direction. The interference note is heard on a loud-speaker or telephone AR. For three-dimensional operation the transmitter may include at least three overlapping differently characterised angularly displaced beams. Three beams may be transmitted in cyclic succession, the first transmitting dots, the second short dashes, and the third long dashes the time between successive transmissions on any one beam being occupied by one transmission on each of the other two in succession. Instead of a single needle indicator V1, there may be employed an intersecting needle indicator having two needles for a twobeam system or three needles for a three-beam system arranged so that their ends enclose an equilateral triangle in the " on course " condition. In the two-needle system the amplitude of the signal governs the rise of the needles so that, in addition to an on-course indication, a distance indication will be given. In the threeneedle system the rise of the needles increases the size of the triangle and thus indicates distance. Instead of using overlapping beams for the directional effect, quasi-optical methods employing reflectors or horns may be used, particularly when relative movement is to be detected and its speed measured. The spread of the directional beam may be made variable so as to vary the field of observation.